ChristianAnswers.Net WebBible Encyclopedia
The term “breastplate” is used to refer to the following two things in the Bible.
That piece of ancient armor that protected the breast. This word is used figuratively in Eph. 6:14 and Isa. 59:17. (See ARMOR.)
An ornament covering the breast of the high priest, first mentioned in Ex. 25:7. It was made of embroidered cloth, set with four rows of precious stones, three in each row. On each stone was engraved the name of one of the twelve tribes (Ex. 28:15-29; 39:8-21). It was in size about ten inches square [25.4 centimeters]. The two upper corners were fastened to the ephod by blue ribbons. It was not to be “loosed from the ephod” (Ex. 28:28). The lower corners were fastened to the girdle of the priest.
As it reminded the priest of his representative character, it was called the memorial (28:29).
It was also called the breastplate of judgment (28:15). (See PRIEST.)